“To pay attention to someone can be a political act,” Aliza Nisenbaum says quietly. For the last four years, the artist has been painting portraits of undocumented immigrants (mostly from Mexico and Central America) in New York City, giving recognition and dignity to individuals who are often obliged to live in the shadows. Her work, in which sensitively rendered figures appear in brightly patterned, semiabstract settings, caught the attention of Whitney Biennial curators Christopher Lew and Mia Locks, and will appear in the exhibition next month. “She’s clearly not painting people she finds on Facebook,” says Lew. “There’s a real back and forth that happens between painter and subject because they know each other so well.”

Aliza, 39, grew up in Mexico City, the child of a Scandinavian-American mother and a Russian Jewish father. (Her name, pronounced “Aleeza,” means “happiness” in Hebrew.) She teaches undergraduate painting and drawing at Columbia—she is also the director of graduate studies in the visual-arts program there—lives in Harlem, and does not yet have a New York gallery, though several are now wooing her. Five years ago, she volunteered to teach a class at Immigrant Movement International, a community space in Queens started by the Cuban-born artist and activist Tania Bruguera. Recognizing that what her mostly Hispanic students really needed was to learn English, Aliza says, “I told Tania I would teach English through feminist art history.” According to Bruguera, Aliza’s “was one of the iconic workshops in the project. In her English classes, using images of art history and women as models, that group not only learned colors, landscapes, and names of objects, they also learned a lot about themselves. In the process it came out that quite a few of the women were going through domestic violence, and because of that, we started another workshop on that subject.”

Aliza’s students responded to her unselfish nature and alert empathy, and they began telling her stories about how they came to America. She got so interested in their lives that she asked many of them if they would sit for portraits, and most were very happy to comply. “Many of the people I painted were used to hiding from visibility. But there’s a kind of mutuality that happens in sitting for a portrait. When you’re painting, you’re looking at every little part of their face, and they would ask me about growing up in Mexico City and how I came here. It’s a very intimate thing.”

Nisenbaum painted Erin with Daisy in the Lobby, 2015, while on an artist’s residency in Knoxville, Tennessee.

All Aliza’s paintings are done from life. She goes to her sitters’ apartments and their children’s birthday parties, incorporates elements of their lives—fabrics, mosaic tile floors, brightly colored walls—and invites them to her place, where she’ll cook for them. She’ll paint the same person multiple times, sometimes alone, sometimes with children, husband, and other family members. “The subjects have a say in how they’re depicted, and what they wear to represent their image,” Aliza says. One man didn’t like his portrait because she’d painted him with stubble, so she painted him again—this time without stubble and wearing his best ostrich-leather boots. From the beginning, she made it clear that she wanted to remunerate her sitters for their time. She offered money or art classes or one of her paintings. “Aliza’s painting of me hangs in my home along with artworks made by my daughter,” says her first model from Immigrant Movement. “She earned my trust almost immediately. We speak the same language—Spanish—and her modesty, kindness, and the way she listens closely made me feel comfortable as soon as I met her.”

Aliza’s own family history is complex. Her great-grandfather David Nisenbaum and his family fled the pogroms in what is now Belarus before World War I and ended up in Mexico because U.S. immigration laws barred their entry. Family lore has it that David sold everything, put the money into a diamond, and brought it over sewn into his daughter’s favorite floppy doll. (She was told to “hold on to it with your life.”) Aliza’s Norwegian great-grandmother Grace Gundmanson Kravik fled an arranged marriage with a 45-year-old man when she was fifteen. She eventually got to Seattle, where she married a Swedish-born ski champion. Aliza’s future parents met on the Paseo de la Reforma in Mexico City. Nancy Anderson, who had inherited her grandmother’s Scandinavian beauty and her willful, adventurous spirit, made an indelible impression on Samuel Nisenbaum. “She was the only platinum blonde he had ever seen,” Aliza says. They married soon afterward and had Aliza and her sister, Karin, four years younger. (Karin went on to be a child star in the internationally famous Mexican telenovela Carrusel.)

La Talaverita, Sunday Morning NY Times, 2016, on show at next month’s Whitney Biennial, portrays Marissa and her father reading the news.

The family lived in a big house in what was then a semirural part of town, where they grew their own vegetables and had a menagerie of ducks, geese, a goat, and many dogs and cats. Karin was passionately fond of animals, but Aliza, from the age of three, cared mostly about art. Her mother made paintings of flowers—large, Georgia O’Keeffe–like blooms—and taught a willing Aliza to draw and paint. “I really admired my mom, who converted to Judaism and was supereccentric and beautiful,” says Aliza. “She wore flower-patterned dresses and didn’t look like anyone else in my environment. It was a very exuberant childhood.” Her father’s leather-goods business took him to New York at least once a year, and he would bring the family along, introducing Aliza to the art world there. “I remember seeing a Lucian Freud show, and a Matisse show at MoMA, and asking my dad to please buy me the Matisse catalog—which I still have.”

Her parents divorced when she was fourteen. Aliza and Karin lived with their father in Mexico and spent summers in St. Louis with their mother and her new husband, a wealthy Mexican-American whose main interest was butterfly hunting. After a two-year foray into psychology, which she studied in Mexico City, Aliza realized that she was much more interested in painting. At the School of the Art Institute of Chicago, where she earned her B.F.A. and M.F.A., she developed a highly personal, intimate style of painting that blurred the line between figuration and abstraction, with bold compositions and flat planes influenced by the great Mexican muralists—Rivera, Orozco, and María Izquierdo, whose work she reveres.

While at the Art Institute, Aliza shared a one-bedroom apartment with her sister, who studied philosophy at the University of Chicago. Karin introduced Aliza to the work of the Lithuanian-French philosopher Emmanuel Levinas, who argued that ethical responsibility and openness to other people were the beginnings of knowledge. “Levinas says that all ethics comes from the face-to-face relationship,” Aliza says, “not from something external.” His thinking has been a major influence on her work and is clearly evident in her many-layered, deeply observed portraits.

Portraits are often said to reveal more about the artist than the subject, but in Aliza’s work, this is not the case—what you see is an open, questing approach, an attempt to understand what cannot ever be fully understood. As Aliza puts it, “The one phenomenon that you can’t really describe is the face of another, somehow. I was so interested in that early on.”

A frequent Nisenbaum subject, the young Mexican woman depicted in Marissa’s Room, 2015, is surrounded by her own artworks, her guitar, and a Virgin Mary calendar serving as protection for her family.

Aliza’s studio is in the second bedroom of her modestly comfortable Harlem apartment. Although she had always wanted to live in New York City, she stayed in Chicago until 2008 because she had a boyfriend there, and a gallery that showed her work, which had moved into large-scale abstract paintings—some of them fourteen feet long. “I was burning to come here the whole time,” Aliza says. “New York is much more like Mexico, much more my sensibility.”

When I visit her in Harlem, three immigrant portraits hang on the studio walls. On the easel is an unfinished still life, one of a series that shows handwritten letters with fanciful drawings on them. In the sitting room, a small portrait of her by the artist Patricia Treib, her closest friend, hangs on the wall. They went to Fort Greene Park in Brooklyn one day in the summer of 2015 and made portraits of each other in the act of painting. “We exchanged them on the spot,” Treib later tells me. “I’ve known her for seventeen years. We were in a drawing class together at the Art Institute of Chicago as undergrads, and I felt this instant kinship.”

Aliza has a small group of friends, whom she sees frequently. She’s still very close to her parents, enjoys windsurfing with her dad in Mexico, and, when we met, was about to go to India for the first time with three of her Nisenbaum aunts. On evenings when she’s not out salsa dancing or at home cooking one of her special Mexican dishes for friends (such as crepes filled with huitlacoche, a delicacy that grows on corn), she spends most of her time reading or painting. She broke up with a longtime boyfriend last summer.

This year, Aliza will turn 40. Neither she nor Karin, who now teaches philosophy at Colgate and who married a year and a half ago, has children yet. “I always thought I was going to be a mom,” Aliza says, “but the opportunity hasn’t presented itself.” She could see herself adopting a child one day. “We have actually talked about whether I could have a child and we could take care of it together,” Karin says, laughing. “We complement each other in really good ways.”

Treib is the one who introduced Aliza to a lot of young New York artists, including Josephine Halvorson and Mira Dancy. “It completely opened my mind to meet those recent Columbia grads who were really engaged with painting—working on easels and en plein air. That revolutionized my thinking, gave me carte blanche to go back into figurative work.”

Cross-stitch, 2015, centers on a handwoven shirt the artist bought in Chiapas, Mexico. To emphasize the labor involved in its making, Nisenbaum filled the background with stitchlike brushstrokes.

The new work turned out to be flower paintings—intense, eleven-by-eight-inch bouquets of gardenias, roses, or peonies (usually whatever she could find at her local bodega). Perhaps they are a nod to her mom’s still lifes, but Aliza’s flowers burst out of the space that encloses them. These paintings led directly to her immigrant portraits, several of which were shown in 2014 at the New York art space White Columns. Three new portraits and the letter painting will be at the Whitney Biennial. Particularly striking is the very large, wonderfully tender canvas of a father and daughter on their turquoise-covered sofa, reading The New York Times. The front page features the police killing last July of a black man in his car, filmed by his girlfriend. Like all of Aliza’s recent works, it’s an indelible image that makes the viewer stop short and spend time with it.

Throughout the world, immigration has recently become an explosive issue, but Aliza could not be accused of latching onto this hot topic as a career move; she started her immigrant portraits more than four years ago, and the way she goes about them is deeply sensitive and far from exploitative. “After coming into close contact with these people through my volunteer teaching and seeing how heroic and inspiring they were to me, I decided to memorialize them in portraits. Revolutionary movements are always made when different people come into solidarity with each other,” she remarks. “I hope my work is more complex than just the issue of immigration.”

Aliza is often frustrated by people who think painting can’t participate in political discourse. “Painting is seen as the market art, and the art that gets seen as political and intellectual is conceptual, nonmaterial work,” she says. Nobody would deny the lasting impact of Goya’s The Third of May 1808 or Picasso’s Guernica, though, and Aliza is convinced that painting—and pictorial beauty—is as relevant today as it has ever been. “Sometimes you can feel that it’s indulgent to make work in the current environment. But I think this is exactly what artists do. They heal, they speak. This is when it’s most urgent to make work. I’m never going to stop painting.”